Microphones that use PZT are well known in the prior art. These microphones typically use so-called bimorphic PZT (A bimorph uses two PZT layers separated by an intermediate conductive layer.) devices that generate small electrical voltages in response to mechanical displacements caused by air pressure changes.
A problem with piezo ceramic microphones however, as well as virtually all other types of microphones, is their susceptibility to mechanical vibrations, which vibrations can themselves cause the ceramic elements in a piezo ceramic microphone to vibrate and thereby produce spurious output voltages. In applications where a microphone is susceptible to mechanical shock, such mechanical shocks can distort or mask particular audio signals of interest.
One potential application for a microphone that must be resistant to mechanical shocks might include for example an active noise cancellation system for an automobile exhaust system. In such a system the sound waves emitted in the exhaust system of an automobile might be effectively cancelled or significantly reduced if the sound waves emitted from the exhaust system are precisely measured and a cancellation wave is produced at a precise instant, which cancellation wave might effectively cancel a sound wave emitted from the automobile exhaust system.
In such an active noise cancellation system, most prior art microphones would likely be unusable because of their susceptibility to electromagnetic interference, vibration, moisture, corrosive exhaust gases, dirt, and heat. A microphone that is more well able to withstand such an environment would be an improvement over the prior art.